I took Powerscore and thought it was useful but here is my advice to you:Take a preptest on your own first. If you score above 160, forget the classes and just get the LR and LG bibles. The classes are very effective if you are having trouble with some of the basics, but if you are already comfortable enough to score a 160+, you will spend a lot of time sitting in a classroom listening to review of things that came naturally to you. This is time that could be better spent self-studying, taking prep tests, and pushing your score up on your own. Just one guy's opinion.
I took a Testmasters prep course for the Sept 2006 test. I needed to improve most in LR. Testmasters doesn't publish ANY LR answer explanations, which makes improvement in LR very difficult. I studied for the Dec. test using Powerscore's LR Bible and LSAC SuperPrep. My score on LR improved immensely once I read explanations. As a result, I have totally lost faith in TM as a good prep course. I think Kaplan and Powerscore are much better options, especially for anyone in the D.C. area (where I'm from).